"Noise" of the simple definition is: "In the process of self-generated signal equipment", these signals are independent of the input signal. Distortion of the signal source to produce the greatest signal strength is not issued simultaneously with the noise intensity as the ratio between the signal to noise ratio, referred to as SNR (Signal / Noise), usually S / N expressed in decibels (dB); noise figure ( M7): refers to the input of the amplifier output signal to noise ratio SNR and 51 datasheet and the ratio of the unit used "dB". The amplifier noise figure is relatively low (such as NF 52. How to understand the output impedance? Much better? either source or amplifier, power supply has output impedance of the problem, the output impedance is a source of resistance. Originally, for an ideal voltage so...